In the manufacture of mercury wetted sealed contact switches, sealing two spaced polepieces into one end of a glass envelope has been found to be a comparatively tedious operation in that the inner ends of the polepieces have to remain precisely positioned opposite to one another after the sealing operation has been completed. Because of the stiffness of the polepieces, an adjustment of the gap after the sealing operation is impractical. The gap between the two polepieces is best set up before and maintained throughout the sealing operation. Consequently, sealing the two polepieces into the envelope has often remained a sequential, operator executed process, even though efficiency advantages of mass sealing operations have been recognized for some time.
Glass diodes, on the other hand, are typically sealed in a mass sealing process wherein the diodes are placed into a graphite holder, and the graphite holder is placed into a controlled atmosphere vessel. Within the vessel, a current is passed through the graphite holder to heat and melt the glass to complete the sealing operation. However, in the diode sealing operation, all of the glass present is typically melted to flow conveniently about the assembly of the leads and the diode chip in forming the sealed diode package. In contrast, sealing the polepieces into the end of the envelope imposes the requirement to maintain the integrity of the cylindrical envelope except for the end portion at which sealing takes place.
U.S. Pat. No. 3,432,282 to P. R. Schulz teaches a method for mass sealing dry reed contacts. The method accomplishes selective melting of both ends of the glass envelope without incurring a meltdown of the center portion of the envelope. The apparatus for accomplishing the method features several component parts. A glass tube carrier of the apparatus is water cooled to maintain portions of the tubes or envelopes in unmelted condition while contact reeds are sealed into the envelope from opposite ends thereof.
The above Schulz patent further teaches a method of adjusting such mass sealed dry reed switches. The insertion of the contact reeds from opposite ends of the envelope and the existence of a central, uncollapsed tubular envelope portion makes it possible to soften the central portion of the envelope and shift the position of the inner ends of the contact reeds with respect to each other. The switches are performance tested as the reed contacts are shifted with respect to each other to determine an optimum setting thereof.
Since a similar adjustment of the two polepieces of the mercury wetted switch with respect to each other after sealing is not practical, it is desirable to precisely position such polepieces during a process of simultaneously sealing a plurality of sets of such polepieces into a respective plurality of envelopes. It is further desirable to achieve selective melting of the envelopes at one end thereof without attaching elaborate cooling provisions to a holder used in the mass assembly of sets of two polepieces into each of the envelopes.